Predicting melanoma metastatic potential by optical and magnetic resonance imaging

Accurate prediction of tumor metastatic potential would be helpful in treatment planning and in the design of agents that modify the tumor phenotype. We report that three methods that are potentially transferable to the clinic - dynamic contrast enhanced MRI (DCE MRI), T_1ρ-weighted imaging and low temperature fluorescence imaging (that could be performed on biopsy specimens) - distinguished between relatively indolent (A375P) and aggressive (C8161) metastatic human melanoma xenografts in nude mice, whereas T₁ and T₂ relaxation time measurements did not. DCE MRI data analyzed by the BOLus Enhanced Relaxation Overview (BOLERO) method in conjunction with concurrent measurements of the arterial input function yielded a blood transfer rate constant (K_trans) which measures perfusion/permeability, that was significantly higher in the core of the indolent tumor than in the core of the aggressive tumor. Histological staining indicated that aggressive tumors had more blood vascular structure but fewer functional vascular structure than indolent tumors. Indolent tumors exhibited T_1ρ values that were significantly higher than those of aggressive tumors at spin-locking frequencies >500Hz. The mitochondrial redox ratio, Fp/(Fp+NADH), where Fp and NADH are the fluorescence of oxidized flavoproteins and reduced pyridine nucleotides, respectively, of aggressive tumors was much higher (more oxidized) than that of indolent tumors and often showed a bimodal distribution with an oxidized core and a reduced rim. These differences observed between these two types of tumors, one indolent and one aggressive, if generalizable, would be very valuable in predicting human melanoma metastatic potential.